1. Field of the Invention
This invention relates generally to the field of resin compositions for a sheet molding compound formulation and, more particularly, to a sheet molding compound formulation for the preparation of enclosures.
2. Description of Related Art
A long-standing problem with fiberglass or plastic electrical enclosures has been their inability to withstand the effects of ultraviolet radiation (UV) from attacking the polymer bond of the fiberglass material when installed in outdoor environments. After a period of time, this UV degradation can cause fiber blooming wherein the polymer material has been broken down and the glass fibers underneath have begun to show through to the surface. Many end users of such fiberglass enclosures view this as visually unappealing, while others view this degradation as having an effect on the physical properties of the material causing a potential failure of the enclosure. Current sheet molding compound (SMC) for enclosures contains brominated resin which, when used with antimony oxide, provides excellent fire retardancy. This type of system used in SMC formulations is also known as a halogenated system. Further, this type of SMC can give off small amounts of toxic emissions and produce black smoke when burned.
Typical SMC using a halogenated base resin system provides excellent chemical resistance and moldability for electrical enclosures. However, most of the halogenated base resin systems used for electrical enclosures lack the necessary chemical bonding strength to withstand the repeated UV attacks on the polymer chains, thereby causing a breakdown of the material which leads to fiber blooming and loss of gloss. Some manufacturers of enclosures have put UV absorbent additives in their current SMC formulations to provide for a small degree of UV resistance. Others have painted the outside of the enclosure, used car wax, or other means of providing protection of the enclosure when installing in outdoor environments. Additionally, some manufacturers have removed bromine from their SMC formulation and have utilized alumina trihydrate (ATH) in greater percentages to allow them to gain the required fire retardancy without the side effects of toxic emissions.
Newer technology such as neopentyl glycol (NPG) based resin systems have provided greater polymer chain bond strength in SMC formulations. These newer technologies in resin development can provide for both chemical resistance and UV resistance in one resin system. This one resin system coupled with the elimination of bromine and increasing amounts of ATH can provide increased protection against UV degradation and maintain the required fire retardancy rating while eliminating the small amounts of toxic emissions that are present in current halogenated resin systems.
It is an object of the present invention to overcome the above deficiencies by providing a UV stable SMC formulation that will provide chemical resistance and extend the usage of the enclosures when installed in outdoor environments. Another object of the present invention is to reduce toxic emissions and black smoke when the sheet molding compound is burned by eliminating the bromine and antimony oxide from within the base resin.
A further object of the present invention is to maintain the flammability ratings recognized within the enclosure industry without the toxic side effects of using a halogenated resin system.